Conventional image recording apparatuses for recording medical images, e.g., CT and MR apparatuses, employ a wet processing system in which a silver salt photographic material is subjected to photographing or recording and then to a wet processing to obtain a reproduced image.
In contrast, a recording apparatus based on a dry processing system not involving a wet processing is recently attracting attention. Examples of such recording apparatuses include an image recording apparatus employing a film of a heat development photosensitive material (hereinafter referred to as "recording film").
In such a heat development photosensitive material recording apparatus, a recording film is irradiated with laser light (exposure) to form a latent image on the recording film. This recording film is heated to thereby develop the latent image. The exposure is generally accomplished by scanning the film with the laser (primary scanning) while controlling the laser output according to image data. It is a matter of course that during this exposure, the recording film is moved in a given direction (secondary scanning). On the other hand, development is generally accomplished by contacting the recording film to a heating member.
Documents dealing with such heat development photosensitive material recording apparatuses include, for example, International Publication WO 95/31754 and International Publication WO 95/30934.
Recording films are produced and packaged under strict quality control so as to eliminate dust particles and other foreign matters therefrom. However, such recording films are used in recording apparatuses which themselves have been installed in the air, and the insides of the apparatuses are open to the air at the time of recording film setting. Hence, the recording apparatuses frequently contain accumulated dust particles and the like which have entered thereinto. As a result, there are cases where dust or other particles adhere to a recording film during the steps of the exposure, development, and conveyance of the recording film.
Such dust or other particles adherent to the film are left in the final step of the recording apparatus, that is, the foreign particles adhere to the heat development part and reside therein. As a result, the foreign particles may damage the recording film or otherwise influence image quality. Despite this, none of the conventional image recording apparatuses has a mechanism for removing dust particles and the like, and there has been a fear from the standpoint of maintaining image quality over long.
On the other hand, image recording apparatuses for recording a medical image on a heat storage type fluorescent sheet, such as digital radiography systems and CT and MR apparatuses, employ a wet system in which a silver salt photographic material is subjected to photographing or recording and then to a wet processing to obtain a reproduced image.
In contrast, a recording apparatus based on a dry system in which a wet processing is not conducted is recently attracting attention. Such recording apparatuses employ a film of a photosensitive and/or thermosensitive recording material (light- and heat-sensitive recording material) or a film of a heat development photosensitive material (hereinafter referred to as "recording material"). In a recording apparatus based on the dry system, a recording material is irradiated with a laser beam in an exposure part (scanning) to form a latent image, and the recording material is then brought into contact with a heating means, e.g., a heating drum, in a heat development part to conduct heat development. Thereafter, the recording material having an image formed thereon is discharged from the apparatus.
Such a dry system is advantageous in that it not only is capable of forming an image in a shorter time period than wet processings, but also is free from the problem of waste water treatment in wet processings. The demand for such dry systems is fully expected to grow in the future.
In the dry system described above, even slight fluctuations of development temperature result in considerably impaired image quality, because the recording material used has higher sensitivity so as to cope with the desired high image quality especially in medical use.
However, there are cases where dust particles which have come into the recording apparatus as a result of recording material conveyance adhere to the surface of the heating drum. This interposition of dust particles between a recording material and the heating drum results in the formation of dot image defects in those areas of the recording material which are in contact with the dust particles.